FIG. 1 is a plan view of the upper surface of an aircraft wing. The wing has a leading edge 1 and a trailing edge 2, each swept to the rear relative to the free stream direction.
At transonic speeds a swept shock 4 forms normal to the upper surface of the wing. As described in Holden, H. A. and Babinsky, H. (2003) Shock/boundary layer interaction control using 3D devices In: 41st Aerospace Sciences Meeting and Exhibit, Jan. 6-9, 2003, Reno, Nev., USA, Paper no. AIAA 2003-447, a 3-D shock bump can be used to induce a smeared shock foot with a lambda-like wave pattern.
Conventionally the chord-wise position of such bumps is dictated by the expected position of the shock 4. However for either laminar or turbulent wings the position is a complex function of Mach number and lift coefficient. The wave drag associated with a shock can be alleviated by the use of a 3-D shock bump that will exhibit maximum benefit when the shock is at a particular location on the bump. Hence as the flight conditions vary the shock may move away from this optimal location.
A traditional approach to solve this problem is to deploy trailing edge variable camber to modify the aerofoil shape and hence the shock location and this incurs additional weight and systems complexity. The challenge then is to find a way of fixing the shock wave independent of the shape of the wing section and the span load distribution.
US 2006/0060720 uses a shock control protrusion to generate a shock extending away from the lower surface of a wing.